An Al Jazeera spokesperson called on Nigerian authorities to release the men without conditions and return their equipment in a press release this morning.

"They have all the relevant paperwork to report on the Nigerian elections and stories related to the election. Both men had just finished filming a story on the military with their cooperation," the spokesperson said.

"Both men are accredited and respected Nigerian journalists.

"As Nigerian citizens they are allowed to travel their country freely."

According to a reported military statement, both men were questioned and restrained in their room because they were operating without "protection, accreditation or due clearance" - despite having just completed filming with the cooperation of the military.

The statement gave a reminder about warnings given to "foreign" journalists, but both Mr Idris and Mr Mustafa are Nigerian nationals.

Both Mr Ahmed and Mr Mustafa are officially accredited by the Independent Electoral Commission in Abuja with the clearance to report from anywhere in Nigeria during the entire election period.

Mr Idris has rich experience reporting in northern Nigeria, and last year he was the first international journalist to reach Chibok and interview families affected by the mass kidnap of schoolgirls by Boko Haram.

Al Jazeera's Ahmed Idris and Ali Mustafa are part of four Al Jazeera English teams reporting on the election in Africa's most populous country and largest economy.